The elevated PT/INR in this patient is most consistent with therapy using which anticoagulant?

The elevated PT/INR in this patient is most consistent with therapy using which anticoagulant?

• A. Heparin
• B. Warfarin
• C. Dabigatran
• D. Rivaroxaban

Answer: (B)

PT/INR measures the extrinsic pathway and is particularly sensitive to warfarin, a vitamin K antagonist. Warfarin inhibits vitamin K–dependent gamma-carboxylation of factors II, VII, IX, and X (and proteins C and S), leading to decreased activity of these clotting factors. Because factor VII has the shortest half-life, the PT/INR rises early during warfarin therapy, making an elevated PT/INR the classic signal of warfarin effect. Heparin mainly prolongs the intrinsic pathway and is monitored by the aPTT rather than the PT/INR. Direct oral anticoagulants like dabigatran and rivaroxaban affect clotting tests in more variable ways and are not routinely monitored with INR.

PT/INR measures the extrinsic pathway and is particularly sensitive to warfarin, a vitamin K antagonist. Warfarin inhibits vitamin K–dependent gamma-carboxylation of factors II, VII, IX, and X (and proteins C and S), leading to decreased activity of these clotting factors. Because factor VII has the shortest half-life, the PT/INR rises early during warfarin therapy, making an elevated PT/INR the classic signal of warfarin effect.

Heparin mainly prolongs the intrinsic pathway and is monitored by the aPTT rather than the PT/INR. Direct oral anticoagulants like dabigatran and rivaroxaban affect clotting tests in more variable ways and are not routinely monitored with INR.